The following circuit diagram shows 1990 Toyota Supra MA70 Fuel System Circuit Diagram. The Fuel system is composed of 3 basic sub systems: Fuel, Air Induction and Electronic Control Systems. The Electronic Control System controls the following functions: Electronic Fuel Injection (EFI); Electronic Spark Advance (ESA); Idle Speed Control (ISC); Diagnosis (detects any malfunctions or abnormalities in the sensor network and lights the "CHECK ENGINE" warning light on the instrument panel); and Fail-safe Function. (click image to enlarge).
The ECU receives signals from various sensors indicating changing engine operating conditions such as: Exhaust oxygen content, Intake air volume, Intake air temperature, Coolant temperature, Engine rpm, Acceleration / deceleration etc. These signals are utilized by the ECU to determine the injection duration necessary for an optimum air-fuel ratio.
The ECU is programmed with data for optimum ignition timing under any and all operating conditions. Using data provided by sensors which monitor various engine functions (rpm, AIC signal, coolant temperature, etc.), the microcomputer (ECU) triggers the spark at precisely the right instant. (See IG section).
The ECU is programmed with target engine speed values to respond to different engine conditions (coolant temperature, air conditioner on/off, etc.). Sensors transmit signals to the ECU which control the flow of air through the by-pass of the throttle valve and adjust idle speed to the target value.